A359213 Numbers k such that rad(k) - 1 is prime.

3, 6, 9, 12, 14, 18, 24, 27, 28, 30, 36, 38, 42, 48, 54, 56, 60, 62, 72, 74, 76, 81, 84, 90, 96, 98, 102, 108, 110, 112, 114, 120, 124, 126, 138, 144, 148, 150, 152, 158, 162, 168, 174, 180, 182, 192, 194, 196, 204, 216, 220, 224, 228, 230, 240, 243, 248, 252

Offset: 1

Author

Arsen Vardanyan, Dec 21 2022

Keywords

• nonn

Examples

			rad(60) - 1 = 2*3*5 - 1 = 29, so 60 is a term.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007947, A097379.

Programs

Mathematica

Select[Range[250], PrimeQ[Times @@ FactorInteger[#][[;; , 1]] - 1] &] (* Amiram Eldar, Dec 21 2022 *)

PARI

isok(k) = isprime(factorback(factor(k)[, 1]) - 1); \\ Michel Marcus, Dec 22 2022